1 Technical Field
The present invention relates to stators and rotating electric machines that include the stators and are used in, for example, motor vehicles as electric motors and electric generators.
2 Description of Related Art
There are known rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators. Those rotating electric machines generally include a rotor and a stator. The stator includes an annular (or hollow cylindrical) stator core and a stator coil. The stator core is disposed in radial opposition to the rotor and has a plurality of slots that are formed in the stator core so as to be spaced from one another in the circumferential direction of the stator core. The stator coil is comprised of a plurality of electric wires that are mounted on the stator core so as to be received in the slots of the stator core.
Japanese Patent Application Publication No. JP2007336725A discloses a first technique of securing the vibration resistance of a stator. Specifically, according to the first technique, a resin adhesive, such as varnish, is filled in the slots of the stator core, thereby fixing the electric wires, which form the stator coil, in the slots. In addition, this patent document also discloses that each of the electric wires forming the stator coil has an insulating coat (or insulating layer) formed on its outer surface. The insulating coat is made of enamel such as an amide-imide (AI) resin or a polyimide (PI) resin.
Japanese Patent Application Publication No. JP2009095167A discloses a second technique of securing the vibration resistance of a stator. Specifically, according to the second technique, a resin adhesive, such as varnish, is applied to a pair of coil end parts of the stator coil which protrude outside the slots respectively from opposite axial end faces of the stator core.
However, during operation of the rotating electric machine, electric current flows in the electric wires forming the stator coil, causing the temperature of the electric wires to be increased due to the electrical resistances thereof. In particular, when the rotating electric machine is used in a motor vehicle where a number of heat-generating machines and devices are installed, the rotating electric machine is subject to a high ambient temperature. Therefore, it is easy for the temperature of the electric wires forming the stator coil to become high. Moreover, the adhesion strength between the resin adhesive and the insulating coats of the electric wires is high. Consequently, when the resin adhesive is cracked by a shock or thermal stress imposed thereon, the insulating coats of the electric wires may also be cracked along with the resin adhesive, resulting in puncture or breakdown of the insulating coats.